set g = the Function of S,T;
set d = the Function of T,S;
take [ the Function of S,T, the Function of T,S] ; :: thesis: ex g being Function of S,T ex d being Function of T,S st [ the Function of S,T, the Function of T,S] = [g,d]
thus ex g being Function of S,T ex d being Function of T,S st [ the Function of S,T, the Function of T,S] = [g,d] ; :: thesis: verum